chemical synapses

chemical synapses include neutotransmitter. It is a chemical synthesized and released from presynaptic nerves. There is a small gap between presynaptic and postsynaptic membrane that is called as synaptic cleft. This cleft is filled with mucopolysaccarides that attaches to the pre-and posysynaptic membranes. The neurotransmitters are stored in the vesicle in thepresynaptic axon end. The axon terminal contains many mitochondria and synaptic vesicles.

The sequence of events during chemical synaptic transmission is :
1- the presynaptic action potential depolarizes the presynaptic membrane. 2- Ca+ permeability increase through the presynaptic membrane.
3-the elevated intracellular Ca+ concentration causes the release of neurotransmitter from synaptic vesicles in to synaptic cleft.
4- Neurotransmitter molecules diffuse across the synaptic cleft to the postsynaptic membrane and they reversibly bind to the specific receptors on the postsynaptic membrane.

Ca is very important in neurotransmitter release . The neuromucular junction is a typical chemical synapse. In this case two acetylcoline molecule are required to open the sodium channel. Postsynaptic membrane include acetycholine esterase to remove ACh.

In each postsynaptic end, a small depolarization is generated. That is called as end plate potential (EPP) or postsynaptic endplate potential.

These mini EPPs reflect the spontaneous release of one, or a few synaptic vesicles. Single EPPs does not generate in chemical synapsis . This ranges from 0.5 msec to 2.0 msec or even more.